Coefficient of thermal expansion of cured epoxy is higher several to tens times than those of ceramic materials and metals. Thus, in the case that an epoxy material is used in conjunction with an inorganic material or a metal, due to different coefficients of thermal expansion between the epoxy material and the inorganic material or between the epoxy material and the metal, the performance and processability of components are significantly limited. For example, in the case of semiconductor packaging or the like, when a silicon wafer and an epoxy substrate are adjacent to each other, due to a significant difference in coefficients of thermal expansion (CTE-mismatch) between constituent components during the processing and/or upon the change of temperatures, the defects, such as cracks, substrate warpage, peeling-off, substrate breakage, and the like, may occur.
Due to such a dimensional change arising from a high CTE of epoxy materials, the developments of next-generation semiconductor substrates, printed circuit boards (PCBs), packaging, organic thin film transistors (OTFT), flexible display substrates, and the like are restricted. Particularly, in the recent semiconductor and PCB industry, the design processing and reliability of next-generation components requiring high levels of integration, miniaturization, flexibility, high performance, and the like may be difficult due to epoxy with a significantly high CTE in comparison with metal/ceramic materials. In other words, in manufacturing components, defects may occur due to relatively high thermal expansion properties of polymer materials at processing temperatures for components, and furthermore, manufacturing processes may be limited. Further, achievements of a design, processability and reliability of components may be problematic. Accordingly, in order to assure the processibility and reliability of electronic components, an epoxy material having improved thermal expansion characteristics, for example, dimensional stability, is required.
To date, (1) the method of making an epoxy composite with inorganic particles (inorganic filler) and/or a fabric, or a (2) the method of designing a novel epoxy compound with a decreased CTE has been generally used, in order to decrease a coefficient of thermal expansion of cured epoxy products.
In the case that an epoxy compound makes composite with inorganic particles as a filler to improve thermal expansion characteristics, a large amount of inorganic silica particles with a diameter of about 2 μm-30 μm is required to reach the low CTE epoxy. However, a problem of the decreased processibility and performance accompanies due to the addition of the a large amount of inorganic particles, In detail, a decrease in fluidity, the formation of voids when narrow gap is filled, and the like, due to a large amount of inorganic particles, may be problematic. In addition, the viscosity of a material may drastically increase due to the addition of inorganic particles. Furthermore, the size of inorganic particles tends to be reduced due to miniaturized semiconductor structures. However, in a case in which fillers with the diameter of 1 μm or less are used, the problem of increased viscosity may become much more severe. Further, in a case in which inorganic particles with a relatively large average diameter are used, the possibility that a composition including a resin and inorganic particles is not properly filled into applied component is increased. On the other hand, in a case in which a composition including an organic resin and a fiber as a filler is used, the CTE may be significantly reduced, but the CTE of composite is still higher as compared to a silicon chip or the like.
Due to the current limitations of composite technology of the aforementioned epoxy resin, the uses thereof in highly integrated, high-performance electronic components, such as next-generation semiconductors and PCBs, and the like, are limited. Therefore, the development of an epoxy composite with the improved thermal expansion properties, for example, a low CTE and high glass transition temperature is required to solve the problems, such as a high CTE in a current thermosetting polymer composite and insufficient heat resistance and processability caused by the high CTE of composite.
Thus, an epoxy compound having an alkoxysilyl group with the heat resistance, for example, a low coefficient of thermal expansion and a high glass transition temperature is disclosed in Korean Patent Application No. 2012-93320 and others, filed by the present inventor. However, when the epoxy compound is only composed of a very reactive alkoxysilyl group, the viscosity thereof may be rapidly increased during making a composite. Therefore, the development of an epoxy compound in which a rapid increase in viscosity during making a composite may be effectively controlled is required.